CW-U and CW-L

V1.3 now has the ability to select either CW-upper sideband or CW-lower sideband in the setup menu. For CW fans, it helps to have an increase in pitch as the slice frequency increases. I take the opposite sideband and set it to the CW pitch frequency. When set this way with wider filter bandwidths, the opposite sideband stays suppressed for really excellent single-signal reception.

Although we've been able to independently adjust the lower and upper filter skirts to null an interfering signal either above or below the operating frequency, now the pitch shift can move in the direction of the operating frequency.

At first, I thought placement would be better in the slice flag, but since the upper and lower skirts are manually set anyway, I see no detriment in leaving it in the setup menu. I have not tried it yet, but hopefully CWU and CWL are captured in the new profiles. Well done!

Paul: Yes the CWL is nice but I don't follow your comment: "I take the opposite sideband and set it to the CW pitch frequency".Let's say my BW is set for 3.0k. To get single signal I have to slide the passband over to the right...Same as before. I'm missing something.

Right. No difference with the new feature except we can now control pitch direction, If I'm set to CW-L and set BW to 3 kHz, I'm now pulling the *upper* sideband back to 600 Hz and leaving it there. Then, the lower sideband is adjusted to the desired Rx bandwidth. It was just the opposite when it was fixed on CW-U.

I agree. I would like to see a setting that automatically pulls in the opposite sideband skirt at or near the CW offset frequency, or something user defined.

In CW, it makes no sense to have perfectly symmetrical skirts at wide bandwidths. We've then lost single-signal ability. Using 600 Hz as an example, then for anything less than 600 Hz, we *would* want equal CW symmetry.

I'd like to better understand your comment, but I'm confused. As I'm sure you know, we let you pick the sideband and then the filters are centered on the pitch frequency in the sideband and the filter skirts reflect this. This just seemed like common sense to me. Are you saying that you would like the skirts to be sharp on one side and not as sharp on the other?

In N4LQ's example, he's right in that when a wide CW filter is selected, (e.g., 3 KHz), the sidebands revert to being symmetrical after the filter button is selected.

Probably the best way to describe this is to go into CW mode, then select the 3 kHz filter, which is the widest preset CW bandwidth setting. Now, tune across a strong CW carrier. Approach the carrier from either direction,. When you do, you will reach zero beat. Then continuing through zero beat, you will hear the opposite sideband come up at the same amplitude as the desired sideband.

Now, click the 3 KHz filter button again. This time, pull the upper sideband to 600 Hz when in CW-L. Try the same sweep though zero beat. As you sweep through zero beat, you will no longer hear the opposite sideband but full audio balance is maintained. The bandwidth has been reduced from 3 kHz to 2.1 kHz: -1500 Hz LSB and +600 Hz USB (instead of +1500 Hz USB). As the selected filter becomes narrower (i.e., below 600 Hz), then sidebands shoukd be symmetrical (as they are now) with no need to offset one against the other for single-signal reception.

Yes, we can do all of this manually and it works great. But as N4LQ points out, every time a wide filter is selected in CW, it reverts back to a symmetrical passband, requiring a manual pulling in of the unwanted sideband.

Hope this made a bit more sense. A hands-on demo would speak many more words!

Let me try this in other words. ... There is no problem as long as the filter width is narrow enough that one side of the symetrical filter is less than the CW offset pitch, (i.e. 500Hz in my case) But if you have a filter set wider than that, the placement of the CW not actually lets you hear on the other side of Zero beat......Requiring the user to shift the filter passband up or down in order to keep the total receive window on one side of the zero beat frequency.....

It would be nice if there was a function that automatically shifted things so that when the filter was too wide it automatically shifted the passband to keep the low end of the filter skirt above zero beat. (or below it, depending upon which "sideband" is selected in setup)

Hi Paul,
Didn't know where to jump in on this topic, but what you are describing is what I want to do with IF shift....that is, shift the entire bandpass to one side or the other of the zero beat freq. The SSB example you describe is essentially the same concept, it puts the bandpass on one side of the zero beat so you don't hear anything from the other sideband. In your example, CW would work the same way as SSB works.....decreasing the CW bandwidth would only move the filter edge farthest away from the zero beat frequency, just as it does in SSB mode.
When the fiter width is very narrow, then the ability to make fine adjustents using IF shift to precisely position the bandpass reative to the zero beat frequency would be outstanding.

One more comment about CW filters. In PowerSDR we had custom filter capability. Since my CW offset was 400 hz, my widest CW filter was 500 hz and I set the upper and lower roll-offs at 150 hz and 650 hz. This centered the filter on my cw offset. As I customized each subsequent filter all the way down to 25 hz, the upper and lower roll-offs were selected to center each filter on my 400 hz CW off-set. This provides the ideal narrow CW filter relationship for your preferred CW off-set. There is no opposite sideband reception with this technique UNLESS you define a filter width greater than twice your CW off-set.

In my case with a 400 hz CW offset, defining. 1200 hz custom filter centered on 400 hz would put the lower edge of the filter 200 hz into the opposite sideband. And if you did this with a 3000 filter, you would be hearing signals 1100 kz into the opposite sideband. This would not be good in a crowded band.

Until we have custom filter capability, switching from filter to filter will always reset the bandpass of the filter symmetrically centered on the CW offset. No problem for filters less than twice the CW offset in width, but it is a problem for any filter significantly wider than twice the CW offset. As Paul said, a demo would be worth a thousand words.

SteveYes that's pretty much it. Most any receiver offsets the passband so when you tune through the signal and cross over the zero-beat point you quickly loose reception. The exception would be a direct conversion receiver where you can hear the cw tone on either sideband. Those are horrible because you can't easily tell which sidetone is correct. What seems even stranger is SSB modes are in fact set up correctly thus rejecting the opposite sideband. Why would a cw op want to hear the other sideband? The system is called "Single-Signal Recption" and it was developed after WWII. Receivers with just a single crystal filter allowed one to adjust the BFO offset away from zero beat and take advantage of the crystal filter which was centered at the IF's frequency. Signals on the opposite side of zero beat were rejected. I can't think of any superhet that didn't work this way until the K3 came along and now the Flex.

Let me add that when we click the 3k bandwidth button, that 3 khz bandwidth should all be on one side of zero. As bandwidth is decreased, only one side of the passband should move toward zero. This way we don't hear stations on the other side of zero beat which can be annoying and confusing.

> "The system is called "Single-Signal Recption" and it was developed after WWII."

Steve, I think single-signal designs went into mass production after WWII, but the concept was first popularized in the early-to-mid 1930s through a series of articles written by James Lamb, then QST's Technical Editor. It was Lamb's single-signal crystal filter that went into the ca. 1935 HRO, then later into the NC-101X. Lamb had a series of articles on the subject through the 1930s. They're works of pure genius.

RIght on Paul...And I mentioned, SSB modes have it right! In fact, it won't let you hear both sidebands at once. CW is actually acting more like AM mode.Paul - When I do as you suggest it does work however somehow my sidetone pitch slider ended up saying 100 instead of the 550 which I had previously set. That's just plain wrong since the pitch coming from my speaker is still 550 hz.

Actually, I like having the filter symetric to the signal, until the filter is so wide that it lets the filter skirt fall below Zero beat. In any case, I hardly ever use anything wider than 500 Hz any more on CW, and usually nothing more than 100-250! It is just so much quieter. And with a 500 Hz offset, I am still good up to 1K bandwidth before it becomes a problem. The only case I can see that would be an exception would be when trying to copy an SSB signal and send CW in return. In this case, the addition of "CW TX while in SSB" mode would solve that one nicely!

FWIW, I had this issue a while back, if I follow what you guys are talking about. On a quiet or dead band, I like wider cw filters. 1, 1.5, or even 3 khz, for example. If you expect to get 'single signal' reception, you must set the pitch much higher than you might be accustomed to; effectively, 1/2 the filter bandwidth. Since I prefer 800 hz, it's not a major problem, except at 3 khz..

OK thanks for all the great explanations. I think the issue is that we didn't anticipate someone using a wide filter with CW. I know some folks prefer this though. Unless I hear otherwise, I have entered an issue in the system to suppress filters crossing DC and instead extend the filter on the other side. So if you were at 500Hz pitch and specified a 2kHz filter, we would go from 0-2kHz instead of -500Hz to 1500Hz. If I'm still not clued in, let me know.

Thanks, I think that is good, Steve. In addition to maintaining "single signal" reception, it will make working crossband CW/SSB possible without using a second slice, too. Which I have occasionally done on 6 Meters. (Until "CW active while in SSB mode" is implemented?)

That results in extremely thin recovered audio with the wider CW filter settings -- and would undermine the goal. I think you had it right the first time when you state: "-500 Hz to 1500 Hz" for a 500 Hz sidetone with a 2 kHz filter. The opposite sideband limit should track the sidetone frequency on the opposite side of zero. The reason for going below the zero point is that the full audio bandwidth of the CW waveform is heard and yet single-signal reception is maintained as long as there's sidetone tracking. When the lower edge is set to zero, the low-end audio response is lost and recovered audio is very "thin."

BTW - Rick Campbell, KK7B, discusses this effect in one of his R2 receiver articles. Quite a bit of effort was spent in maximizing analog opposite rejection while providing a flat audio response down to below 100 Hz. Let me know, and I'll dig it up if its of interest.

The primary reason for the wider CW bandwidth is to judge the overall quality of the received CW waveform and at the same time, get a feel for what's happening in and around the center frequency. For others, narrow CW filter settings can be fatiguing over time.

I realize that CW ops who only use narrow filters won't get this concept. At the narrow settings of 500 Hz and lower, the filters should be left just as they are since single-signal reception is guaranteed. Hope this helps.

I'm not sure I get it, and will need to read the article. But if there are operators who like it this way, I would suggest that this could be a click-box option in the CW set up tab? That way it could be customized to fit each op's preference. (I am a multiple options kind of guy...) <grin>

I'm not certain we're talking about the same thing. We have to decide whether we are talking about audio or RF. When you put your pitch at 600Hz, we essentially shift the filter you have up by that about. So a 200Hz filter is really 500-700Hz. If your pitch is at 500Hz and we set the RF filter to -500 to 1500Hz, you will have sidebands from -500 to 500 mixing in the audio space. In other words a tone at -200 sounds the same as a tone at 200. The rule, based on what I THINK I said was that in CW-U the low edge of the filter cannot go more than <pitch>Hz below the carrier indicator in the display (this frequency in the demodulator is 0Hz). Is this correct or am I still lost in space?

The last thing I want is to come across like I'm asking Flex to design my own radio. It's probably best to experiment with some of these choices. As long as the skirts can be independently varied as they are now, that's what's most important.

I think you got it, steve. Some of us, who listen with wider filter widths on quiet, or 'dead' bands, prefer true 'single signal' reception, regardless of pitch setting or filter width. I don't want to hear signals on the other side of zero beat; or, have an irritatingly hi pitch setting, either.

You got it right now Steve. The way it's set up now is really DSB Double sideband on CW. It should be SSB. I should never be able to hear the image of the other sideband. Even so, having passband tuning like PSDR was handy.

I like to open the filter up as wide as possible and listen to as much of the cw band as my hearing range allows. The dynamic range on these rigs is amazing. My brain is able to pick out and lock on to one of multitudes of tones. The signals don't mush together as they do on conventional radios.

N5FD Bruce Thanks Paul for the last paragraph "I realize that CW ops won't get this concept............should be left just as they at since single-signal reception is guaranteed"And yes this helps. Although The concept might be understood but not applicable to one who never uses a filter greater than 100 Hz. and has never connected his mike. Thanks again Paul. 73,Bruce N5FD

p.s. Love my Flex and it's filters best in my 55 years as a CW op in USN and amateur radio.

Steve......I can imagine this is getting confusing. Your example of a wide filter with one edge below zero beat allowing a tone at -200 hz to sound the same as a tone at +200 hz is EXACTLY what we DO NOT want to happen. I (we) NEVER want to hear signals from the opposite side band. In a CW contest, that's another station's run frequency. I don't want to hear him or any stations calling him. I think you have it right if you apply the SSB analogy of never letting the edge of the filter go below zero beat (to the opposite sideband).

If someone wants to listen to what is below zero beat, engage the RIT and go there. Or, let the op grab the lower edge of the filter skirt and drag it below zero beat.

Keep the filter symmetrical on the CW offset until the filter width approaches twice the CW offset, then any additional filter width gets added to the high side of the filter, just like in SSB mode. Vice-versa for LSB CW mode.

Steve, I'll throw my comments in here as well. When using a "filter" that would exceed 1/2 the pitch frequency toward the zero beat side, I'd cap it at that and allow the non zero beat side to extend either the rest of the selected filter bandwidth or 1/2 the selected filter bandwidth. In the former, the filter width away from zero beat would vary based on the pitch while in the latter, it is always equal to 1/2 the selected width, or "1500" for a 3.0K. It's not really a 3.0k filter at that point, but a 1.5k plus 1/2 the pitch. Yes, most contesters "running" will use a wider filter to not miss someone calling way off frequency, but you don't want to hear the station operating next to you that may be 1 KHz away from your frequency.

This also addresses the sound of the "filter" and removes the undesirable "bassy" sound from it.

And I've just played around more with pitches of 700, 500 and 400. I like that a filter of 1.0 is 1.0. That is 1/2 the pitch from spot towards zero beat and the remainder away. So for the three pitches, that's 350 Hz lower than spot and 650 Hz above spot, 250 Hz lower than spot and 750 Hz above, and finally 200 Hz below spot and 800 Hz above.

Setting the lower limit to zero for wide CW bandwidths is better than it currently is. For those of us who want to pull it across zero to match the side-tone frequency, it just takes a tug with the mouse.

PaulYes but if you're using LSB or USB tugging the mouse won't drag the sideband past zero for some reason. Seems to me like you should be able to expand it either way or both. Isn't that how Psdr worked?

Not sure how it was in PSDR since the 6700 is my first Flex. In either USB or LSB, there's no need to set the filter below zero. In CW the issue is affected by the offset and we must extend beyond zero. The offset is a function of the selected side-tone frequency.

K5UA's formula is the right one. K5UA's Axiom: "Keep the filter symmetrical on the CW offset until the filter width approaches twice the CW offset, then any additional filter width gets added to the high side of the filter, just like in SSB mode. Vice-versa for LSB CW mode."

As an example of the need to go below the zero point for wide CW filter settings (wide is defined as more than 2x the CW offset), let's select the 3 kHz CW filter in SSDR. Presently the 3K CW is a symmetrical passband at -1500 Hz and +1500 Hz. Now, as proposed by some, let's take the opposite sideband (determined by the new CW-L/CW-U menu feature) and bring it to zero. For CW-U, keep the right side untouched at +1500 Hz, now bring the lower side from -1500 to exactly 0. Now listen. Pretty awful, isn't it. There's no way anyone can listen to that audio passband. If that becomes the default setting, it will generate a lot of complaints. This is not the same as bringing the lower limit to zero in USB or LSB. Hate to mix audio into the discussion, but the audio passband is a function of the DSP passband.

The right way: For the 3 kHz CW filter and a 600 Hz offset chosen in SSDR, 2x the offset is a 1.2K filter. Since half of the 3K filter is 1500 Hz, we have well exceeded the symmetry threshold. For a 600 Hz offset, the symmetry threshold is a 1.2K filter (-600/+600). Since 3K is more than 2x the offset (1.2K), then we keep the offset amount intact on the undesired sideband. That's -600 Hz for CW-U. Since 3K is more than 2x the offset, the additional bandwidth most go to the high side. We end up with -600 Hz and +2400 Hz for a 3K filter. The bandwidth is 3K and single-signal reception is intact. We get exactly what we want from the wider CW filter: (1) the desired wide bandwidth with full passband audio; and (2) single-signal reception.

Probably the best way to understand this is to use my example above and move the filter skirts while listening to a CW QSO. One experiment is worth a thousand words.

Last night I was listening to the CW portion of 40m with the filter at 3 khz. Heard a guy calling CQ right on frequency. Started to call him until I realized he was on the wrong side of zero-beat! That couldn't happen with any other receiver. This needs fixin.

All levity aside, after all the manhours spent designing narrow analog crystal filters over the years, and after all the manhours recently spent refining skirts on digital filters in SDR radios, I have trouble envisioning anyone listening to CW in a filter wider than 500 hz. There could be quite a few stations dispersed in a 500 hz bandwidth on a busy frequency, not to mention a 1500 hz bandwidth. My mission to to isolate the desired CW signal for maximum signal to noise ratio amd maximum readibility.

I don't understand the efficacy of using wide CW bandwidths, which will degrade signal to noise of the desired signal by introducing more band noise, or worse, add competiting signals in the bandwidth which will add to the processing load on your brain. To use a SSB analogy, you would not use a 6 khz filter in a crowded band to listen to a 3 khz station, would you? Then why would you use a wide filter in the CW analogy?

I just don't see the practical application of wide CW filters in a panadapter capable radio where you can SEE adjacent CW signals without having to suffer the misery of hearing them.

CharlesClose your eyes and listen to a 25 khz wide chunk of the CW spectrum and let the melodious calliope emanating from the ethereal heavens permeate your soul as it wafts through your mind. Gradually your understand will come to light and you will come to despise the raucous racket of an unnecessarily narrow filter and learn to use such a device only when necessary.

You are absolutely correct Steve, there is a harmonically displeasing penalty of using an unnecessarily narrow CW filter, the key word being unnecessarily. And you are correct again, it should only be used when necessary. This is why I typically use a 400 hz filter as my standard CW filter on an uncrowded band, and 100 hz on a crowded band.

My definition of torture is not water-boarding, it would be listening to CW on a 1500 hz filter under any band conditions, crowded or dead.

For me, there is just too much high frequency hiss in the bandpass of a wide CW filter (i.e., greater than 500 hz). It may not bother someone if they have a high frequency hearing loss (a biologic filter), but it drives me to distraction to hear all that high frequency hiss mixed in with what I am trying to hear at my CW offset of 400 hz.

Fortunately, once again.... isn't it great we have a F..L..E..X..I..B..L..E radio?

On the other hand... As one who usually listens to CW with nothing less than 250 Hz filters on the 6500, there is a different, less tiresome effect when listening to a strong CW signal with AGC on MED or SLOW and the AGC-T turned down low so that there is NO noise other than the CW signal. It is similar to listening to ESSB on the low end of 80 with strong signals and low RF gain.... Quiet and relaxing with no noise and high fidelity signals that stand out against the noise. Yet in a crowded band with more noise, or with higher AGC-T the wide filter would bust my brain!

In any case, I agree that Flexibility is key, which we already have with the ability to grab and slide the filter. I do agree with others that wider filters should default to settings that keep the low end above zero beat. But for those who like to keep the filters symmetrical even below the zero beat, they should be able to drag them there.

I tend to run with pitch at 700hz and when tuning around use the 800hz BW setting. In my case this is not really an issue. With this type of rig, my first Flex, I tend to point and click. I am getting pretty good and usually click with a few hertz of center passband. As soon as I start the QSO I go to 50 hz unless it is a round table.

When I was NTS for 2RN and handled a lot of CW traffic I ran with a wide BW filter setting so that Stations that QNI would be heard by me even if they were way off QRG.

Personally, I would prefer to keep the filter system just as it is even if I would ever go wide BW and possibly be tuning on the wrong side of the CW signal. If wide I always verify which side I am on by slightly tuning the VFO and see which way the pitch goes. There maybe times when I need to sit on a QRG and be able to hear wide BW on both sides such as listening for a weak DX signal that may not be on QRG.

I think a good solution would be, if it is decided to modify the CW filters to a non-symmetrical state, please allow a menu selection for both methods.

One of the nice features of a SDR System is it is easy to add menu selections for the old method and the proposed new method. That way CW operators who like the present system will not lose out.

By the way Steve and the gang did a great job on the CW fixes. On transmit we are clean on transmit to 100 wpm, CWL works, and the Red LED on the front panel never stays Red during receive. We currently have the best QSK of any rig out there.